1. Field of the Invention
The present invention relates to the disposal of oil and gas well proppant used during the drilling and production of an oil and gas well, wherein a fluid carries excess proppant to a removal area at the well head for separating proppant from the fluid. Even more particularly, the present invention relates to an improved proppant recovery system that collects the excess proppant to later be reused with new proppant.
2. Description of the Related Art
Proppant, e.g., sand, is pumped into wellbore fractures to increase the surface area of the fracture. The increased surface area allows for increased production from the fracture. However, not all of the proppant pumped into the wellbore deposits into the fracture. Instead, some of the proppant remains in the wellbore. This excess proppant must be removed from the wellbore for production from the fracture.
A typical well is designed with up to 10 proppant-fractured zones. The stimulation technique involves the pumping of as much as 300,000 pounds of proppant into each zone. During this process up to 70,000 pounds of excess proppant may remain in the wellbore, which is cleaned out using coiled tubing. The proppant material contains a resin coating to facilitate adhesion in the reservoir, which restricts disposal.
Previously, this excess proppant had to be collected offshore, placed in big bags, contained and shipped to shore for incineration. This practice was costly, wasteful, and environmentally suspect. Engineering studies revealed that the properties of the excess proppant made it suitable to be re-cycled in future operations with minimal impact on fracture performance. While re-using proppant has become an accepted practice with no noticeable effect on well productivity, logistically it had some limitations. The material still had to be collected offshore and transported onshore where it was stored for several months before being reloaded into the stimulation vessel for reuse in the next fracture treatment. This represents storage problems and environmental contamination problems associated with exposure of these materials. Furthermore, even with no unforeseen delays, this was still a time consuming, e.g., 24-hour, two-way trip.
What is desired is a way to recycle the excess proppant in a manner that saves cost. It is also advantageous for the recycle system to be more simple logistically than previous recycle systems. Ideally, but not necessarily, the recovery system would operate entirely on-site without having to transport the excess proppant off-site for processing. Despite the apparent advantages of such a recovery system, to date no such recovery system has been commercially introduced.